VS 2008 - Pass JSON String To Download Page

I've got code like this in a download page

Code:
Imports System.IO
Imports System.Data
Imports System.Data.SqlClient
Partial Class _Download
Inherits System.Web.UI.Page

[Code] .....

That is called like this:

Code:
function excelGrid(strId, blnDoReader) {
var wesPC = $("#" + strId);
var objWebParam = {};
var arrGrid = [];

[Code] ....

I am modifying this now - passing in the variable strWebParam which is the "stringified" version of a JSON array. And then in the function below I am trying to get the JSON-string into the POST. I tried the INPUT/TYPE=HIDDEN method you see below - but that did not work (cut off the string - it's got quotes in it)

Code:
$.downloadExcel = function(url, data, source, method, callback) {
var inputs = '';
var iframeX;
var downloadInterval;
if (url && data) {

[Code] ....

When I do a regular AJAX post for something I use the "data" element of the $.ajax method like this

Code:
var strWebParam = $.toJSON(objWebParam);
$.ajax({
type: "POST",
url: "WebService.asmx/BootPage",
dataType: "json",

[Code] .....

How is that DATA: STRWEBPARAM getting passed back to IIS??